1. Field of the Invention
The present invention relates to a hybrid vehicle, and in particular to a hybrid vehicle of 4 wheel-drive (4WD) type in which front wheels are driven by an engine, while rear wheels are driven by motors.
2. Description of the Related Art
Conventionally known is a hybrid vehicle in which the driving force of an engine is assisted by motors. Among hybrid vehicles of this type there exists a parallel hybrid vehicle in which a motor/generator is provided in parallel with an engine, whereby in acceleration of the vehicle the motor/generator is operated as a motor for assisting the engine, while in deceleration of the vehicle the motor/generator is operated as a generator for charging the battery (for instance, refer to Japanese Unexamined Patent Publication No. HEI 9-140006 which discloses a similar technology). In addition, a simple hybrid vehicle is studied in which a few improvements are carried out on a mass-produced gasoline-fueled vehicle such that rear wheels thereof are rendered assist by motors which are run by a conventional 12V battery.
Then, as is disclosed in Japanese Unexamined Patent Publication No. HEI 8-237811, there is provided a hybrid vehicle in which a 12V battery is charged with electric power obtained by driving a generator with an engine, and rear motors are driven with the electric output power of the battery, wherein there are disposed two such batteries, whereby in normal driving, the two batteries are used in parallel (12V), while in running the motors at high revolutions, the two batteries are connected in series (24V) to increase the driving voltage.
With the first related art hybrid vehicle in which the motor/generator is provided, however, since the motor/generator is selectively used as a motor or a generator, there is caused a problem that driving of the vehicle and generation of electricity cannot be performed simultaneously. In addition, for instance, with a front engine vehicle, the motor/generator is coupled to a front-mounted engine and thus it has to be disposed at a front side of the vehicle, this causing a problem that the degree of freedom in layout becomes low.
On the other hand, in the second related art simple hybrid vehicle in which the rear wheels are rendered assist by the motors, since the motors are driven at 12V, the motor current becomes large, and power loss in wires becomes great, this therefore causing a problem that wiring has to be implemented using thick wires.
Then, with the third related art rear wheel assisted type hybrid vehicle, the motor driving voltage can be increased, but since the generator remains at the low voltage, this also suffers from the aforesaid problem of large power loss throughout the wiring.
Thus, an object of the present invention is to provide a hybrid vehicle that can provide a high degree of freedom in layout as a hybrid vehicle and which can obviate the necessity of using thick wires for wiring by increasing the voltage.
With a view to attaining the above object, there is provided a hybrid vehicle including an engine (for instance, an engine 2 described in a mode of operation of the present invention that will be described hereinafter) for driving first driving wheels, a generator (for instance, a generator 6 in the mode of operation of the invention) adapted to be driven by the engine for generation at a first voltage (for instance, 42V described in the same mode); a first battery (for instance, a battery 11 in the mode of operation of the invention) adapted to be charged with a generated output from the generator; motors (for instance, motors 8 described in the mode of operation of the invention) for driving second driving wheels (for instance, rear wheels 7 in the same mode) with a generated output from the generator; a direct-current voltage converter (for instance, a direct-current voltage converter 12 described in the mode of operation of the invention) for allowing the generated output to step down to a second voltage (for instance, 14V described in the same mode) that is lower than the first voltage; and a second battery (for instance, a battery 13 for accessories described in the mode of operation of the invention) and an electric load (for instance, an electric load 14 described in the same mode), the second battery being adapted to be supplied with electric power at the voltage allowed to step down by the direct-current voltage converter.
According to the construction described above, when the engine is driven, the generator allows the motors to drive the second-driving wheels at the first voltage which is higher than the second voltage to thereby give assist to the engine. Then, the generated output of the generator is caused to step down to the second voltage by means of the direct-current voltage converter and the voltage so caused to step down is then supplied to the second battery for distribution to various types of electric loads.
Further, driving by the motors can be stopped when the motors are detected as abnormal.
With this construction, even when the motors are in an abnormal state, the second battery and the electric load can be supplied as usual with electric power via the direct-current voltage converter.